Photofabrication is a general term for technologies to produce various precision parts by a series of steps in which:
a radiation-sensitive resin composition is applied onto a workpiece surface;
the resultant film is patterned by photolithography; and
a chemical etching or an electroforming technique, mainly comprising an electrolytic etching or an electroplating, or their combination is carried out using the patterned film as a mask. This photofabrication is now a mainstream technology in the production of precision and fine parts.
In these years, the downsizing of electronic devices has accelerated a high integration and multi-layering of larger scale integration (LSI). To cope with such miniaturization, it is required that an LSI is mounted by a high pin count on a substrate to install in electronic devices. As such mounting technologies, bare chip mounting technologies, for example TAB mounting and flip-chip mounting, have more and more attracted attention. In the high density mounting, metal conductors formed by electrolytic plating have strict requirements. For example, one of the requirements is micropatterning of the metal conductors. Such metal patterns include bumps, called microelectrodes, and wirings that form conductive paths to electrodes. These metal patterns are required to be more microscopic with the trends toward the miniaturization, high pin counting and multi-layering of the package. For example, as the conventional projecting microelectrodes, gold bumps of about 20 μm high are arranged at a pitch of 40 μm or more with a distance of 8 to 10 μm between the bump edges. However, the bump pitches are required to be smaller because of higher performance and smaller size of electronic devices, and now the bump pitch of 25 μm is demanded.
Radiation-sensitive resin compositions used in the production of such microscopic metal patterns are required:
to form a radiation-sensitive film in a thickness greater than a deposit thickness necessary to from a bump, and to have a high resolution,
for example, to have a resolution whereby the resultant film in a thickness of 20 μm or more can be patterned at 25 μm pitches in the production of gold bumps; or a resolution whereby the resultant film in a thickness of 10 μm can be patterned at 5 μm pitches in the formation of wirings.
Further, a patterned product which is obtained by curing the radiation-sensitive resin composition is used as a mask in electrolytic plating. Then, the patterned product is required to have a sufficient wettability by plating solutions and have a plating resistance. Further, it is necessary that patterned product can be easily and completely stripped by a stripping solution or the like without damaging the metal pattern given after plating.
However, the conventional radiation-sensitive resin compositions for metal pattern production hardly satisfy both the sufficient resolution and the other properties, such as plating resistance. When the resin composition has a poor resolution, a desired microscopic metal pattern is hardly formed and semiconductor devices with such metal patterns cannot be produced. Further, when the wettability is poor, a plating solution will not be supplied in a sufficient amount within the microscopic pattern of the cured product. Therefore, the metal pattern cannot be formed. Also, a poor plating resistance causes a short circuit between conductive parts, and the device may not operate properly.